C++ LVILatticeVal::mergeIn方法代码示例

bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
                                                PHINode *PN, BasicBlock *BB) {
  LVILatticeVal Result;  // Start Undefined.

  // Loop over all of our predecessors, merging what we know from them into
  // result.
  bool EdgesMissing = false;
  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
    BasicBlock *PhiBB = PN->getIncomingBlock(i);
    Value *PhiVal = PN->getIncomingValue(i);
    LVILatticeVal EdgeResult;
    EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult);
    if (EdgesMissing)
      continue;

    Result.mergeIn(EdgeResult);

    // If we hit overdefined, exit early.  The BlockVals entry is already set
    // to overdefined.
    if (Result.isOverdefined()) {
      DEBUG(dbgs() << " compute BB '" << BB->getName()
            << "' - overdefined because of pred.\n");
      
      BBLV = Result;
      return true;
    }
  }
  if (EdgesMissing)
    return false;

  // Return the merged value, which is more precise than 'overdefined'.
  assert(!Result.isOverdefined() && "Possible PHI in entry block?");
  BBLV = Result;
  return true;
}

// If we can determine a constant range for the value Val in the context
// provided by the instruction BBI, then merge it into BBLV. If we did find a
// constant range, return true.
void LazyValueInfoCache::mergeAssumeBlockValueConstantRange(Value *Val,
                                                            LVILatticeVal &BBLV,
                                                            Instruction *BBI) {
  BBI = BBI ? BBI : dyn_cast<Instruction>(Val);
  if (!BBI)
    return;

  for (auto &AssumeVH : AC->assumptions()) {
    if (!AssumeVH)
      continue;
    auto *I = cast<CallInst>(AssumeVH);
    if (!isValidAssumeForContext(I, BBI, DL, DT))
      continue;

    Value *C = I->getArgOperand(0);
    if (ICmpInst *ICI = dyn_cast<ICmpInst>(C)) {
      LVILatticeVal Result;
      if (getValueFromFromCondition(Val, ICI, Result)) {
        if (BBLV.isOverdefined())
          BBLV = Result;
        else
          BBLV.mergeIn(Result);
      }
    }
  }
}

bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
                                                 Value *Val, BasicBlock *BB) {
  LVILatticeVal Result;  // Start Undefined.

  // If this is a pointer, and there's a load from that pointer in this BB,
  // then we know that the pointer can't be NULL.
  bool NotNull = false;
  if (Val->getType()->isPointerTy()) {
    if (isKnownNonNull(Val)) {
      NotNull = true;
    } else {
      Value *UnderlyingVal = GetUnderlyingObject(Val);
      // If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
      // inside InstructionDereferencesPointer either.
      if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, NULL, 1)) {
        for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
             BI != BE; ++BI) {
          if (InstructionDereferencesPointer(BI, UnderlyingVal)) {
            NotNull = true;
            break;
          }
        }
      }
    }
  }

  // If this is the entry block, we must be asking about an argument.  The
  // value is overdefined.
  if (BB == &BB->getParent()->getEntryBlock()) {
    assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
    if (NotNull) {
      PointerType *PTy = cast<PointerType>(Val->getType());
      Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
    } else {
      Result.markOverdefined();
    }
    BBLV = Result;
    return true;
  }

  // Loop over all of our predecessors, merging what we know from them into
  // result.
  bool EdgesMissing = false;
  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
    LVILatticeVal EdgeResult;
    EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
    if (EdgesMissing)
      continue;

    Result.mergeIn(EdgeResult);

    // If we hit overdefined, exit early.  The BlockVals entry is already set
    // to overdefined.
    if (Result.isOverdefined()) {
      DEBUG(dbgs() << " compute BB '" << BB->getName()
            << "' - overdefined because of pred.\n");
      // If we previously determined that this is a pointer that can't be null
      // then return that rather than giving up entirely.
      if (NotNull) {
        PointerType *PTy = cast<PointerType>(Val->getType());
        Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
      }
      
      BBLV = Result;
      return true;
    }
  }
  if (EdgesMissing)
    return false;

  // Return the merged value, which is more precise than 'overdefined'.
  assert(!Result.isOverdefined());
  BBLV = Result;
  return true;
}

LVILatticeVal LVIQuery::getBlockValue(BasicBlock *BB) {
  // See if we already have a value for this block.
  LVILatticeVal BBLV = getCachedEntryForBlock(BB);
  
  // If we've already computed this block's value, return it.
  if (!BBLV.isUndefined()) {
    DEBUG(dbgs() << "  reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
    return BBLV;
  }

  // Otherwise, this is the first time we're seeing this block.  Reset the
  // lattice value to overdefined, so that cycles will terminate and be
  // conservatively correct.
  BBLV.markOverdefined();
  Cache[BB] = BBLV;
  
  Instruction *BBI = dyn_cast<Instruction>(Val);
  if (BBI == 0 || BBI->getParent() != BB) {
    LVILatticeVal Result;  // Start Undefined.
    
    // If this is a pointer, and there's a load from that pointer in this BB,
    // then we know that the pointer can't be NULL.
    bool NotNull = false;
    if (Val->getType()->isPointerTy()) {
      for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();BI != BE;++BI){
        LoadInst *L = dyn_cast<LoadInst>(BI);
        if (L && L->getPointerAddressSpace() == 0 &&
            L->getPointerOperand()->getUnderlyingObject() ==
              Val->getUnderlyingObject()) {
          NotNull = true;
          break;
        }
      }
    }
    
    unsigned NumPreds = 0;    
    // Loop over all of our predecessors, merging what we know from them into
    // result.
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
      Result.mergeIn(getEdgeValue(*PI, BB));
      
      // If we hit overdefined, exit early.  The BlockVals entry is already set
      // to overdefined.
      if (Result.isOverdefined()) {
        DEBUG(dbgs() << " compute BB '" << BB->getName()
                     << "' - overdefined because of pred.\n");
        // If we previously determined that this is a pointer that can't be null
        // then return that rather than giving up entirely.
        if (NotNull) {
          const PointerType *PTy = cast<PointerType>(Val->getType());
          Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
        }
        
        return Result;
      }
      ++NumPreds;
    }
    
    
    // If this is the entry block, we must be asking about an argument.  The
    // value is overdefined.
    if (NumPreds == 0 && BB == &BB->getParent()->front()) {
      assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
      Result.markOverdefined();
      return Result;
    }
    
    // Return the merged value, which is more precise than 'overdefined'.
    assert(!Result.isOverdefined());
    return Cache[BB] = Result;
  }
  
  // If this value is defined by an instruction in this block, we have to
  // process it here somehow or return overdefined.
  if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
    LVILatticeVal Result;  // Start Undefined.
    
    // Loop over all of our predecessors, merging what we know from them into
    // result.
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
      Value* PhiVal = PN->getIncomingValueForBlock(*PI);
      Result.mergeIn(Parent.getValueOnEdge(PhiVal, *PI, BB));
      
      // If we hit overdefined, exit early.  The BlockVals entry is already set
      // to overdefined.
      if (Result.isOverdefined()) {
        DEBUG(dbgs() << " compute BB '" << BB->getName()
                     << "' - overdefined because of pred.\n");
        return Result;
      }
    }
    
    // Return the merged value, which is more precise than 'overdefined'.
    assert(!Result.isOverdefined());
    return Cache[BB] = Result;
  }

  assert(Cache[BB].isOverdefined() && "Recursive query changed our cache?");

  // We can only analyze the definitions of certain classes of instructions
//.........这里部分代码省略.........

bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
  if (isa<Constant>(Val))
    return true;

  if (hasCachedValueInfo(Val, BB)) {
    // If we have a cached value, use that.
    DEBUG(dbgs() << "  reuse BB '" << BB->getName()
                 << "' val=" << getCachedValueInfo(Val, BB) << '\n');

    // Since we're reusing a cached value, we don't need to update the
    // OverDefinedCache. The cache will have been properly updated whenever the
    // cached value was inserted.
    return true;
  }

  // Hold off inserting this value into the Cache in case we have to return
  // false and come back later.
  LVILatticeVal Res;

  Instruction *BBI = dyn_cast<Instruction>(Val);
  if (!BBI || BBI->getParent() != BB) {
    if (!solveBlockValueNonLocal(Res, Val, BB))
      return false;
   insertResult(Val, BB, Res);
   return true;
  }

  if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
    if (!solveBlockValuePHINode(Res, PN, BB))
      return false;
    insertResult(Val, BB, Res);
    return true;
  }

  // If this value is a nonnull pointer, record it's range and bailout.
  PointerType *PT = dyn_cast<PointerType>(BBI->getType());
  if (PT && isKnownNonNull(BBI)) {
    Res = LVILatticeVal::getNot(ConstantPointerNull::get(PT));
    insertResult(Val, BB, Res);
    return true;
  }

  // If this is an instruction which supports range metadata, return the
  // implied range.  TODO: This should be an intersection, not a union.
  Res.mergeIn(getFromRangeMetadata(BBI), DL);

  // We can only analyze the definitions of certain classes of instructions
  // (integral binops and casts at the moment), so bail if this isn't one.
  LVILatticeVal Result;
  if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
     !BBI->getType()->isIntegerTy()) {
    DEBUG(dbgs() << " compute BB '" << BB->getName()
                 << "' - overdefined because inst def found.\n");
    Res.markOverdefined();
    insertResult(Val, BB, Res);
    return true;
  }

  // FIXME: We're currently limited to binops with a constant RHS.  This should
  // be improved.
  BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
  if (BO && !isa<ConstantInt>(BO->getOperand(1))) { 
    DEBUG(dbgs() << " compute BB '" << BB->getName()
                 << "' - overdefined because inst def found.\n");

    Res.markOverdefined();
    insertResult(Val, BB, Res);
    return true;
  }

  if (!solveBlockValueConstantRange(Res, BBI, BB))
    return false;
  insertResult(Val, BB, Res);
  return true;
}